Solid-Sate Magma in Dormant Volcanoes Can Quickly Liquefy and Become Active

Magma beneath Oregon's Mount Hood has been in relative cold storage for thousands of years, entombed in a near-solid state beneath the mountain. But the coagulated magma can liquefy rapidly and with just a minor temperature increase, according to new research led by Oregon State University scientists.

The block of magma can liquefy in just a couple month's time when it becomes heated to more than 750 degrees Celsius, which can happen when hot magma from deep within the Earth's crust rises to the surface. It is this very such mixing of magmas that led to Mt. Hood's last two eruptions, which occurred about 220 and 1,500 years ago.

"If the temperature of the rock is too cold, the magma is like peanut butter in a refrigerator," said Adam Kent, an Oregon State University geologist and co-author of the study. "It just isn't very mobile. For Mount Hood, the threshold seems to be about 750 degrees C -- if it warms up just 50 to 75 degrees above that, it greatly increases the viscosity of the magma and makes it easier to mobilize."

Kent and his colleagues are interested in the temperature at which the magma resides in the Earth's crust beneath the mountain because it could provide insights into when Mt. Hood - which is informally considered dormant - could erupt again and what type of eruption it could be.

"What we found was that the magma has been stored beneath Mt. Hood for at least 20,000 years -- and probably more like 100,000 years," Kent said. "And during the time it's been there, it's been in cold storage -- like the peanut butter in the fridge -- a minimum of 88 percent of the time, and likely more than 99 percent of the time."

The researchers contend that Mt. Hood's solid magma can quickly be heated to the temperature it needs to be viscous, but that most of the time the magma - which lies about 5 kilometers (3 miles) beneath the surface - is held under conditions that make it difficult to erupt.

"What is encouraging from another standpoint is that modern technology should be able to detect when magma is beginning to liquefy, or mobilize," Kent said, "and that may give us warning of a potential eruption. Monitoring gases, utilizing seismic waves and studying ground deformation through GPS are a few of the techniques that could tell us that things are warming."

By further studying the temperatures required for magma to shift from its solid state to liquid, volcanologists will be able to make better forecasts for volcanic activity.

Kent and his colleagues published their work in the journal Nature.